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Full text of "The Cambridge Natural History"

DEFINITION    OF   THE   CLASS

actors might he used in addition to those which will be made
use" of in the following brief catalogue of essential mammalian
features, were it not for the low-placed Monotremata on the one
hand and the highly specialised Whales 011 the other. Including
those forms, the Mammalia are to be distinguished from all other
Vertebrates by the following series of structural features, which
will he expanded later into a short disquisition upon the general
structure of the Mammalia. The class Mammalia may, in fact, be
thus defined :---
Hair-clad Vertebrates, with cutaneous glands in the female,
secreting milk for the nourishment of the young. Skull without
prefrontul, post frontal, qitadrato-jugal, and some other bones, and
with two occipital condyles formed entirely by the exoccipitals.
"Lower jaw composed of dciitary bone only, articulating only with
the s<]uamo8al. Kar bones a chain of three or four separate bonelets.
Cervical vertebrae sharply distinguished from the dorsals, and if
with free ribs, showing no transition bet woo n these and who
thoracic ribs. [Bruin, with four optic lobes. .Lungs and heart
separated from abdominal cavity by a muwular diaphragm. "Heart
with a single left aortic arch. lied blood-curpnF.rlcs non-nuc-loji.tt».
The following   characters   are   also   very iifarJy inuvor.saj, a,nd
in   any  ca.se   absolutely   diKtinetivt' :---Otirvioal   vort.^brao,   seven;
vertebrae with epiphytes. Ankle-John '*" c'ruro-tiuvjil," ?.r. be-
tween tlie leg and the ankle, and. not in the middle of the ankle.1
Attachment of the pelvis to the vertebral coluiH.fi pre-ucetubitlar
in position.
The Mammalia >smee they are hot-Hoot!r-d t»rt«iturft« are more
independent of temperature than reptik'R ; they ?m>. thtm fouml
Hpread over a wider area of tins ca-rthV Huricu*.(\ AK h* .vv-uver, though
hot-blooded, they have not tin*. j*ower.H of lowmoti*'*u ]»ott8e«aetl by
birds, they are not quite HO widely distiibiiUHl as arc-* thofte
animals. The IVfanimiilia nuij.v*. up uit-o tho i.»xtivr^<» luifUi. but,
cxcoptiug only forms inauily *,Ujiu»,tu(. such tin the Sea. JJ^Bfci,, are not
known to occur on tho .Antarctic, continent'. "Witii tho i's<
of the flying Hats, indigcmoiiB tuanirnalH art',* totally alwcm
Hew Zealand; and it seem** to be <Ii>ul>tt*ul whether tho#e sup-
posed oceanic islands which have a xnajatznttliaiL fUima really
1 Tiic dege»eratlon of tlie hiwd-li?Hb in,Wti»lr» awl Bwtjsi* foi'l«*ls fcl» *»e of
tMs cl»»ira€ter w m 4iHtinefcive o»e on tUo pTiaelplefe ?ntvo««,ie<i "by tlut tfelaoti^m of
tii« above liat. But it would bo absurd to leaw u»ut lialr.